New product and use thereof

ABSTRACT

A new pre-alloyed metal based powder, intended to be used in surface coating of metal parts. The powder is deposited using e.g. laser cladding or plasma transfer arc welding (PTA), or thermal spray (e.g. HVOF). The powder is useful for reducing friction and improving wear reducing properties of the deposited coating. Such coatings may also improve machinability. As friction or wear reducing component, inclusions of manganese sulphide or tungsten sulphide in the pre-alloyed powder may be used.

FIELD OF THE INVENTION

The present invention relates to a new pre-alloyed metal based powder,intended to be used in surface coating of metal parts. The powder isdeposited using e.g. laser cladding or plasma transfer arc welding(PTA), or thermal spray (e.g. HVOF). The powder is useful for reducingfriction and improving wear reducing properties of the depositedcoating. Such coatings may also improve machinability. As friction orwear reducing component, inclusions of manganese sulphide or tungstensulphide in the pre-alloyed powder may be used.

BACKGROUND

Thermal surfacing i.e. thermal spray coating and overlay welding powdergrades are widely used for coating of component surfaces against wearand corrosion. Fe-, Ni- and Co-based grades are known to radicallyimprove life time of wear- and/or corrosion exposed components. However,there is still a large number of applications where component life timesneed to be improved. In addition, high prices and limited availabilityof Ni and Co on the world market also calls for longer life timeimprovement. Finally, development of new coating deposition methods likelaser cladding, cold spraying and high velocity spraying open newpossibilities for alloying, more accurate control of coating process andhigher automation, thereby calling for additional types of powders.

A potential approach to improve friction and wear properties may be toincorporate solid lubricant to thermal surfacing grades so that thedeposited coating includes friction and wear reducing substances whilemaintaining acceptable levels of corrosion resistance and hardness.

Solid lubricants are soft solid phase materials which are capable ofreducing friction and wear between two surfaces sliding against eachother without the need for a liquid media. Materials to be considered assolid lubricants need to meet at least the following criteria: adherecontacting surfaces—stickiness: low shear strength—low intrinsicfriction; low hardness—low abrasivity and thermochemical stability forthe intended environment. Examples of solid lubricants are; talc,graphite, manganese sulphide (MnS), molybdenum disulphide (MoS₂), ortungsten disulphide (WS₂). Use of solid lubricants may provideadvantages in: stability at extremely low or high temperatures;stability in extreme environments, such as cold or hot environments, orenvironments having high radiation levels; mechanical design issues(lighter design, reduced critical velocity) or able to carry extremeloads.

For a long time, the use of solid lubricants in thermal surfacing hasbeen a difficult proposition, the reason being that numerous solidlubricants are metal sulphides and that even trace amounts of sulphur inwelds can lead to cracking and/or corrosion.

Skarvelis et al; ASME J. Tribol. 132 (2010) 031302-1-031302-8, Surf. &Coat. Techn. 203 (2009) 1384-1394, and Trib. Int. 42 (2009) 1765-1770describe the use of mixing MnS powder with a metal powder and using theresulting powder mix in e.g. PTA (plasma transferred arc welding).

Solid lubricants, however may have high friction coefficient compared tothat of oil or grease; finite wear life for solid lubricant films whenrenewal is not possible; no or limited cooling capacity compared to oilor grease, or tendency to clogging caused by debris and residualparticles.

SUMMARY OF THE INVENTION

Surprisingly, the inventors have noticed that solid lubricants, whenpresent as inclusions in a pre-alloyed metal powder, display a betterlubricating effect than when the solid lubricant is present as a powdercomponent in a powder mixture. The present invention relates to a metalpowder which is pre-alloyed with a solid lubricant (e.g. MnS or WS₂),and the use of the metal powder for coating the surface of a substrate.The main benefit of using a solid lubricant according to the inventionis longer life time in wear- and/or corrosion exposed components.

FIGURES

FIG. 1 Friction coefficient (COF) and wear in a coating made by using anMnS-powder pre-mixed with a metal alloy powder.

FIG. 2 Friction coefficient (COF) and wear in a coating made by using apre-alloyed metal powder having inclusions of MnS.

FIG. 3 SEM micrograph of a particle of 1525-30 SP570 +5% MnS prealloyedpowder. Dark grey areas are inclusions containing of MnS.

FIG. 4 Slider on sheet wear. Slider on stainless steel sheettribocontact, normal load 10N, sliding velocity 0.36 m/s, dry (notlubricated). Y-axis shows coefficient of friction, and X-axis showssliding distance.

DETAILED DESCRIPTION

The present inventors have shown that manganese sulphide, MnS, is asuitable solid lubricant. The results show a potential for friction andwear reduction by Mn and S which is prealloyed to metal powder . Thepowder pre-alloyed with Mn and S is especially well suited for weldcladding methods, such as laser cladding or PTA. In addition, thermalspray, e.g. flame spray, HVOF, HVAF, coldspray, plasma spray, and thelike may also be suitable applications. Machinability assessed throughplane grinding of test is unaltered for alloyed grades made frompre-alloyed metal powder having MnS inclusions, compared to metal alloyswithout solid lubricant inclusions.

All percentages herein are % by weight.

In one aspect, the invention provides a composition of a pre-alloyedmetal powder which comprises manganese sulphide (MnS) or tungstensulphide (WS2) inclusions. The term “pre-alloyed”, as used herein,denotes a metal powder, the powder particles of which have inclusions ofe.g. MnS and/or WS2, i.e. Mn and/or W, and S, have been included in themelt when preparing the pre-alloyed powder.

Metal powder alloys suitable for use according to the present inventionare typically nickel, iron, or cobalt based.

Consequently, one embodiment of the invention is a composition of apre-alloyed nickel based metal powder alloy, containing or consisting ofC, 0.05-0.4%; Si, 2.0-3.1; B, 0.6-1.5; Cr, 2.6-3.6; Fe, 1.2-2.5; Al,0.2-0.7; inclusions of MnS, 4-15%; the balance being Ni.

A further embodiment of the invention is a composition of a pre-alloyedcobalt based metal powder alloy, containing or consisting of C,0.05-0.4%; Si, 2.0-3.1; B, 0.6-1.5; Cr, 2.6-3.6; Fe, 1.2-2.5; Al,0.2-0.7; inclusions of MnS, 4-15%; the balance being Co.

A further embodiment of the invention is a composition or a pre-alloyediron based metal powder containing or consisting of 1-1.3% C, 1-1.3%;Cr, 22-27%; Mn, 4-5%; Ni, 3-5%; Si, 3-4%; Mo, 1.5-2.5%; inclusions ofMnS 4-15%; the balance being Fe.

A further embodiment of the invention is a composition of a pre-alloyednickel based metal powder alloy, containing or consisting of C,0.05-0.2%; Si, 2.2-2.9; B, 0.8-1.3; Cr, 2.8-3.45; Fe, 1.4-2.3; Al,0.3-0.5; inclusions of MnS, 4-15%; the balance being Ni.

A further embodiment of the invention is a composition of a pre-alloyedcobalt based metal powder alloy, containing or consisting of C,0.05-0.2%; Si, 2.2-2.9; B, 0.8-1.3; Cr, 2.8-3.45; Fe, 1.4-2.3; Al,0.3-0.5; inclusions of MnS, 4-15%; the balance being Co.

A further embodiment of the invention is a composition or a pre-alloyediron based metal powder containing or consisting of 1.2% C, 1.2%; Cr,25%; Mn, 4.5%; Ni, 4%; Si, 3.3%; Mo, 2%; inclusions of MnS 4-15%; thebalance being Fe.

In one embodiment, the amount of MnS and/or WS₂ in the form ofinclusions is 4-8%, or 5-8%, by weight.

The prealloyed nickel, iron, or cobalt based powder is preferablyproduced by water or gas atomization of a melt which includes Mn or W, Sand other alloying elements chosen from the group consisting of C, Si,B, Cr, Fe, Al, Ni, Co, and V.

The particle size of the pre-alloyed powder alloy is typically from 10μm to 800 μm, or from 10 μm to 200 μm, or preferably from 15-150 μm, or50-150 μm.

The solid lubricant (e.g. MnS or WS₂) is present as inclusions. Theseinclusions are made by adding the solid lubricant (e.g. MnS or WS₂) tothe molten metal as is, or alternatively, FeS may be mixed withappropriate amounts of FeMn and then adding to the molten metal.

In one aspect, the invention provides a method for surface coating metalparts, by way of deposition techniques such as laser cladding or PTA(plasma transferred arc); thermal spray methods such as HVOF (highvelocity oxy fuel spray), HVAF (high velocity acetylene fuel spray) orplasma spray; or by slurry methods such as centrifugal casting, with theabove mentioned metal powder.

In one embodiment, the invention provides the use according to theabove, wherein said metal powder contains 4-10%, or 4-8%, or 5-7% byweight of MnS or WS2 as inclusions.

In a further aspect, the invention also provides metal parts produced bythe above mentioned suitable for coating by the powder according to theinvention for dry friction contacts in machinery, such ase.g. industrialvalves, sheet metal forming (SMF) tools, transport rollers in ironworks, paper knives, and glass moulds.

EXAMPLES Example 1

Preparation of Pre-Alloyed Powder A metal powder was prepared asfollows; a metal powder with the following composition; C, 0.05-0.2%;Si, 2.2-2.9%; B, 0.8-1.3%; Cr, 2.8-3.45%; Fe, 1.4-2.3%; Al, 0.3-0.5%;MnS, 4-15%; the balance being Ni, was prepared by atomisation of a meltcontaining the elements above in said amounts. The resulting powdercontains MnS as inclusions in a matrix of metal alloy. This powder isherein denoted “Powder A”.

Example 2

Preparation of pre-mixed powder was done by mixing a pre-alloyed metalpowder with the following composition; C, 0.05-0.2%; Si, 2.2-2.9%; B,0.8-1.3%; Cr, 2.8-3.45%; Fe, 1.4-2.3%; Al, 0.3-0.5%, with 5 wt % MnSpowder in a common powder mixer. This powder is herein denoted “PowderB”.

Example 3 Application of Powder by Deposition Using PTA

Pre-alloyed or pre-mixed powder was applied to test samples as follows;Powder A was deposited onto S235JRG (base structural steel) substrateplates by PTA (plasma transfer arc) with parameters set to allow for adilution of 5-15%.

Example 4

Powder B was spread by hand on substrate as a powder before fusing withthe substrate.

Example 5

Powder according to the invention was also applied to substrate by lasercladding. Solid lubricant (MnS) inclusions appeared in coatings frompowder A and from powder B. The coating from Powder A appears to resultin finer inclusion sizes of MnS than those from Powder B.

Example 6 Wear Testing

Wear testing was performed, and shows the beneficial effects of Powder Ain a metal surface coating layer or clad. The specimens were hardfacedrectangular blocks where the base metal was commonly used low carbonstructural steel (EN S235 JRG, ASTM A570 Gr.36) and the surface layerwas at least 1 mm thick in the as finished measure. The test surface hada ground finish with surface roughness of Ra 0.3-0.4 μm, prepared byboth plane grinding. The counters Ø60/CR100×17 rings are made of AISI316L (EN X2CrNiMo17 12 2) or AISI 304L (EN X2CrNi19-9) stainless steel.The friction test was unlubricated i.e. dry, and the test samples werecarefully cleaned and degreased by ethanol prior to testing. Weartesting was analogous to the testing described in standard ASTM G77. Thetest maximum Hertzian contact pressure was 180 MPa, angular velocity was0.36 m/s and the total sliding distance was 594 m.

Example 7 Slider on Sheet Wear Testing

Slider on sheet wear testing was performed, and shows the beneficialeffects of Powder A in a metal surface coating layer or clad. Thespecimens were cylindrical rings ø50/CR5 mx 10 mm where the base metalwas commonly used low carbon structural steel (EN S235 JRG, ASTM A570Gr.36) and the surface layer was at least 0.5 mm thick in the asfinished measure. The test surface had a ground finish with surfaceroughness of Ra 0.3-0.4 μm, prepared by both OD grinding. The counterssheets 1000×1000×1.5 mm were made of AISI 316L (EN X2CrNiMo17 12 2)stainless steel. The friction test was unlubricated i.e. dry, and thetest samples were carefully cleaned and then degreased by ethanol priorto testing. The test normal load was 10 N, sliding velocity was 0.36 m/sand the total sliding distance was 3 m. Results are shown in FIG. 4.

Example 8 Corrosion Testing

Outcome of salt spray corrosion testing according to ISO 16701 wasperformed. The parts were macrophotographed at each interval, after 12,15, 30 and 39 days. Subsequently, a SEM (scanning electron microscopy)investigation was done. Coating layers from Powder B exhibited an arrayof 50 μm rust hills after 39 days. The rust initiation was distinguishedat 12 days' stop. Coating layers from Powder A achieved a similar typeof rust but the number of the rusty hills was much fewer, and the sizesof these were smaller. Quantification of the results may be made bypixelizing the SEM-micrographs, using image analysis software such asAdobe Photoshop.

1. Water or gas atomized metal powder containing or consisting ofcomprising, by weight: C, 0.05-0.2%; Si, 2.2-2.9; B, 0.8-1.3; Cr,2.8-3.45; Fe, 1.4-2.3; Al, 0.3-0.5; inclusions of MnS, 4-15%; thebalance being Ni, said powder being suitable for thermal surfacing. 2.Water or gas atomized metal powder comprising, by weight: C, 0.05-0.2%;Si, 2.2-2.9; B, 0.8-1.3; Cr, 2.8-3.45; Fe, 1.4-2.3; Al, 0.3-0.5;inclusions of MnS, 4-15%; the balance being Co, said powder beingsuitable for thermal surfacing.
 3. Water or gas atomized metal powdercontaining or consisting of comprising, by weight: C, 1.2%; Cr, 25%; Mn,4.5%; Ni, 4%; Si, 3.3%; Mo, 2%; inclusions of MnS 4-15%; the balancebeing Fe, said powder being suitable for thermal surfacing.
 4. Metalpowder according to claim 1, wherein the amount of MnS is 4-8% byweight.
 5. Metal powder according to claim 1, wherein the particle sizeof the prealloyed powder alloy is from 45 μm to 200 mm.
 6. Method forsurface coating metal parts, by way of laser cladding or PTA (plasmatransferred arc), with a metal powder according to claim 1, therebyproducing a metal coated component.
 7. Metal coated component producedby the method according to claim
 6. 8. Metal coated component accordingto claim 7, wherein the component is chosen from the group consisting ofindustrial valves, sheet metal forming (SMF) tools, transport rollers iniron works, paper knifes, and glass moulds.
 9. Metal powder according toclaim 1, the metal powder consisting of, by weight: C, 0.05-0.2%; Si,2.2-2.9; B, 0.8-1.3; Cr, 2.8-3.45; Fe, 1.4-2.3; Al, 0.3-0.5; inclusionsof MnS, 4-15%; the balance being Ni.
 10. Metal powder according to claim2, the metal powder consisting of, by weight: C, 0.05-0.2%; Si, 2.2-2.9;B, 0.8-1.3; Cr, 2.8-3.45; Fe, 1.4-2.3; Al, 0.3-0.5; inclusions of MnS,4-15%; the balance being Co.
 11. Metal powder according to claim 1, themetal powder consisting of, by weight: C, 1.2%; Cr, 25%; Mn, 4.5%; Ni,4%; Si, 3.3%; Mo, 2%; inclusions of MnS 4-15%; the balance being Fe. 12.Metal powder according to claim 1, wherein the amount of MnS is 5-7%, byweight.
 13. Metal powder according to claim 1, wherein the particle sizeof the prealloyed powder alloy is from 50-150 μm.